Recently, the performance of compact wireless devices such as mobile phones has been greatly improved, and compact wireless devices ready for non-contact IC cards, such as IC cards compliant with NFC (Near Field Communication) Standard, specifically, MIFARE and Felica, have come on the market. Such a compact wireless device is loaded with a non-contact communication antenna (hereinafter referred to as a proximity antenna) in a frequency of MHz band.
In such a proximity antenna, a spiral coil having several-turns formed on a print substrate by etching is generally used (see, for example, Japanese Patent Application Laid-Open Publication No. 2005-93867). The reason why the spiral coil is provided with the several turns is because less than several turns precludes sufficient communication characteristics. In addition, there is also known an example of a proximity antenna formed by winding a wire several times On the inner surface of a cabinet of a compact wireless device. However, in this type of proximity antenna, the shape thereof may be liable to be collapsed, the antenna characteristics thereof may be liable to be dispersed, and a communication distance may be shortened.
Aside from this, as one of resonator structures, a structure called interdigital coupling is known. In the interdigital coupling, a pair of sheet-shaped resonators are disposed in proximity to each other so that the open ends (signal supply ends) of the resonators face the short-circuit ends thereof, and the interdigital coupling has a feature in that a frequency is separated to a high resonance frequency and a low resonance frequency centering around the resonance frequency of simple resonators. (In what follows, The separated state is called a composite resonance mode.) When the low resonance frequency is used as an operating frequency, an interdigital coupling resonator can more reduce its length than the length of respective resonators when they are used as simple resonators as well as can be obtain good balance characteristics. Further, a conductor loss is also reduced. What has been mentioned above is described in detail in Paragraphs 0038 to 0055 of Japanese Patent Application Laid-Open Publication No. 2007-60618.
With improving the performance of such compact wireless devices, the number of components used has been increased steadily. In such circumstances, the above-mentioned proximity antenna, for example, has a vertical length of 40 mm, a horizontal length of 30 mm, and a wiring width of 4 mm for three-turns and thus occupies a very large area as a component carried by the compact wireless device and reduces the installation area of other component. In addition, such a proximity antenna has a problem in that the antenna characteristics thereof are deteriorated only by a metal component located near to the proximity antenna (in particular, located just under a coil conductor), and this is a difficult problem in a layout of components.